NS

1
NSE HLW - Class 4

• Cs purification
• Sr purification
• Separations and encapsulation occurred at Hanford
  from late 60s to late 70s
• Work from the Gasper authored handout
• Ken Gasper was Program Manager of the
  Encapsulation Project circa 1977 and 1983

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Wastes processed

• Table 2-1 Hanford specific definitions
• Note curie concentrations, up to 1900 Ci/gal
• Note chemical composition, Mostly Na and NOx(-)
  (NO2- and NO3-)
• Except for CAW, the Hanford wastes (feedstocks to
  the Cs Sr separations) were neutralized, hence
  strongly (2 to 5 molar) NaNO3 NaNO2 rich as
  they all are today
• With a strong NaOH solution, pH10, most metals
  have precipitated as oxides and hydroxides.

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B Plant
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Process development approach

• Page 27
• Pilot scale
• Pilot plant scale
• At issue is the high radiation levels which
  inhibit fixing equipment or modifying equipment
  configuration after going radioactive (a.k.a.,
  hot)
• We will go through each treatment process

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How do we separate chemicals?

• By using PHASE changes
• Solubility differences Liquid to Solid
• This is the preferred method for large quantities
• Vapor pressure differences -Evaporation
• Mineral formation
• Ion exchange Solid ion exchange media or
  solvent solvent extraction
• Mass differences (diffusion, mass spectrometers,
  chromatography)
• Most importantly, any phase separation

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Fission products

• Cs is virtually the only monovalent - Group 1,
  fission product. Look on Chart of Nuclides,
  Periodic Table, for any others. Rubidium is the
  only other fission product, but not much of it.
• Most fission products are valence 2 or
  multi-valent, exceptions are Yttrium and
  Lanthanum
• Thus, the first alternative for separation should
  be separating valence 1 and 2 chemicals.

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Hanford Waste Tanks
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West Area Tank Farms
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Tank farm under construction
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Cs separation from CAW

• CAW is acid, and most things (metal ions) are in
  solution
• CAW has minimal sodium, because, as CAW, it has
  not yet been neutralized
• To separate, one needs either a precipitation
  agent selective for Cs precipitate everything
  but Cs or find a selective ion exchange agent.
• Phosphotungstic acid (PTA), H3PW12O40 was used
• Both Cs3PW12O40 (H2O) and Cs2HPW12O40(2H2O) are
  insoluble and few other phosphotungstates are
  insoluble (page 35).

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Cs PTA process

• Principally Cs, rubidium, and ammonium
  precipitated, with some Na and K precipitated.
• Now you can separate liquid and solid phases
• Wash the precipitates with dilute nitric acid and
  sodium gluconate (an industrial cleaner, see
  http//www.jungbunzlauer.com/products/product_24.h
  tmlgeneral-info )
• Then digest in 2M NaOH which destroys the PTA and
  dissolves the Cs

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Cs purification

• Page-41 81 MCi recovered in 4 years
• Safety concerns may develop later on.
• Page 39 -note the use of zeolite ion exchange
  media for Cs separation
• Note the use of ammonium as a stripping agent
• Observe the simplicity of Cs purification vs. Sr
  purification, due mostly to valence states of
  most of the waste contaminants.
• Initially they used zeolite resins, later
  switched to ARC-359, an organic
• West Valley chose to go with a zeolite resin

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Cs concentration

• Issues - separability and stability against
  radiation
• Final purification used a zeolite resin. Why?
  Because the radiation fields were so high they
  would destroy most organic resins.
• Note competition between Na and K as the resin
  loadings get higher. Note problems with
  radiolysis.
• Ion exchange column 10.5 cu ft loaded to 0.8 MCi
• Product was loaded out as Cs2CO3
• Product concentration of 40 kCi/gal leads to
  serious heating, evaporation, and radiolysis.

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Strontium separation

• The book is a little confusing, since all of
  these processes were used, in different sequences
• The sulfate strike precipitates Sr from many
  different waste streams
• The sulfate/hydroxide/carbonate metatheses
  process can remove many metals.
• Hydroxide precipitation at pH10 results in 96
  pure Sr
• Solvent solvent extraction was used in place of
  the sulfate/hydroxide/carbonate metatheses for
  the precipitation process waste streams.

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Sr separation

• (Sr salts are extremely insoluble, particularly
  SrSO4)
• Mostly begins with neutralization of acid wastes.
  Sr precipitates out as the nitrate, hydroxide,
  carbonate, or sulfate
• Page 50, initial solid feed is 0.0003 M Sr or
  300 ppm, comparable to Ca in drinking water and
  2 Molar Na. See also pp 17 and 19. That Ca,
  for the most part was never removed.
• When starting with CAW, precipitate out the 2
  ions with sulfate.

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Sr Metathesis process

• page 33 - Washed sludges
• Much of the Sr began as SrSO4
• The carbonate metathesis process was used hot
  NaOH and NaCO3
• This process (metathesis) digested the Sr solids
  and selectively converted SrSO4 to carbonate,
  leaving many other valence 2 salts as sulfates.
  Clearly not all, since other ions dominated.
• Weak nitric acid now selectively dissolves SrCO3

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Sr solvent-solvent extraction

• pp. 49 66 Begin with solvent solvent
  extraction
• Aqueous Sr Nitrate solution add EDTA, HEDTA,
  and citric acid to keep many of the other metal
  ions in aqueous phase
• Organic phase was normal paraffin hydrocarbon
  (NPH) much like kerosene with an extractant
  D2EHPA and TBP (see page 53)
• How do you know what extractant to use? That is
  the art and requires much lab work. Try and try
  until you find one that works.

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Sr purification solvent-solvent extraction

• Pages 52-55
• First contact moves all ions but single valent
  ions (Na) to organic phase (well, not all, but
  lots!)
• Column 1S removes more Na from organic (some
  makes it over)
• Third contact puts Sr in aqueous phase and
  keeps Ca, Mn, and RE in organic
• Fourth contact cleans up organic phase
• Sr concentrate is still as much as 501 Na
• Recall it began as much as 50,0001

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Sr caustic strike

• pp. 60 6- ff
• Caustic strike removed 90 or the remaining
  metals, except Na, Ca, and Ba
• The trick here is that most hydroxides are
  insoluble, except for Sr(OH)2 which is soluble at
  pH 10
• It is now 96-99 Sr except for Na (50) Na is
  irrelevant because in the final step, SrF2 will
  be precipitated from a NaF, 8 molar NaOH solution.

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Rare earth strike and Ba removal

• Page 64 Rare Earth strike to recover Sr from
  the above waste streams.
• Ba removal, if necessary, based on chromate
  solubilities (p. 70)

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Sr purification conclusion

• Sr can be separated and purified
• It is a much more difficult task because of all
  the competition with other di-valent or
  apparently di-valent ions, plus an initial
  500001 NaSr ratio

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Secondary waste streams

• Page 71
• 400 kgal/month BCS (steam condensate)
• 1.4 Mgal/month BCP (process condensate)
• 70 Mgal/month cooling water
• 9.5 Mgal/month chemical sewer

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Resource chemicals

• p.80
• Note
• The addition of all of these organic chemicals,
  HEDTA, EDTA, Na-Gluconate, and Citric Acid in
  particular, resulted in their current
  double-shell slurry and the infamous burping
  tank 101-SY

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Encapsulation

• The objective was to produce inert salts (at
  least gas-free salts) and then store these in
  double walled, corrosion resistant, metal capsules

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Final solidification of Cs

• Cs was purified to Cs2CO3
• p. 93 Boil all remaining water, and then add
  concentrated HCl to convert
• Cs2CO3 2HCl gt 2CsCl CO2 H2O
• (a gas which evaporates a liquid and a solid in
  solution)
• The CsCl is left in a aqueous solution
• This was then boiled dry, melted and poured into
  a capsule, a straight-forward and simple operation

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Cs Product

• 53 wt Cs (Table 2.22, probably a little wrong
  since Cl 25 of CsCl something is off in Table
  2.22 from Table 2.9, it should be more like 65-70
  wt
• Dry, solidified from a melt (high density)
• Cs-133 52.9 54.4 (Stable)
• Cs-134 0.000 0.005
• Cs-135 11.4 12.8
• Cs-137 34.2 34.3

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Cs Capsules

• 49.5 MCi of Cs-137 chloride are stored in 1311
  capsules, each of which is 2.6 inches in outside
  diameter and 20.8 inches long (from a CBD)
  density of CsCl 3.98 g/cc
• About 2 - 3 kg of material
• See p. 104

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Final solidification of Sr

• Sr was purified to SrNO3
• The pH was adjusted to 10 with NaOH and powdered
  NaF was added
• SrNO3 2NaF gt SrF2 NaNO3
• The SrF2 precipitates and must be filtered
• The strontium fluoride does not melt, but rather
  was fired and sintered. It was more like
  caramelizing sugar.

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Sr Product

• About 65 wt Sr (27 wt F)
• 57 of the Sr was Sr-90
• all capsules must remain at least 6 feet
  underwater in the existing WESF pools, one of
  which is 8.8 feet wide by 21.8 feet long by 10.8
  feet deep and the remaining 7 pools each being
  4.4 feet wide by 21.8 feet long by 10.8 feet
  deep.

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Sr Capsules

• 21.4 MCi of Sr-90 fluoride are stored in 601
  capsules, each of which is 2.6 inches in diameter
  and 20.1 inches long. Density of SrF (crystal)
  4.24 g/cc
• About 2 kg each Although SrF has a higher
  crystal density, it could not be poured into the
  capsule, loosing about a factor of 0.4 for
  packing factor.

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Encapsulation

• Product Quality p.112
• Economics - p. 119 Buck-a-curie (1984 dollars)
• From p. 131, any current costs should be
  3-4/ciinflationtighter restrictionslicensing
• inflation x3 (Y2K)
• tighter restrictions x4
• licensing 500 M min

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Alternatives

• p. 156
• Pb2SO4 carrier
• D2EHPA solvent extraction
• Ion exchange
• Zeolite ion exchange (WVDP)
• Metal ferrocyanide precipitation (Cs)
• Sodium tetraphenyl borate (current SRP process)